Download your desired IPSW iOS from http://forums.team-nocturnal.com/index.php?/forum/48-ios-releases/ or https://ipsw.me/
Put your phone into recovery mode
iPhone 7 method
Turn Off your iPhone 7 if it isn't off already.
Press and hold down the On/Off button on the right side for 3 seconds.
Swipe the slide to power off confirmation slider to the right.
Press and hold down the volume down button on your iPhone 7.
Plug your iPhone 7 into your Mac or Windows PC and make sure iTunes is running.
Release the volume down button when you see the Connect to iTunes screen
iPhone 6 and older Method
Turn Off your iPhone, iPod touch, or iPad if it isn't off already.
Press and hold down the On/Off button on the right side (iPhone 6 or later) or top (all other iPhones, iPods, and iPads) for 3 seconds.
Swipe the slide to power off confirmation slider to the right.
Press and hold down the Home button on your iPhone, iPod touch, or iPhone.
Plug your iPhone, iPod touch, or iPad into your Mac or Windows PC and make sure iTunes is running.
Release the Home button when you see the Connect to iTunes screen.
iTunes
Plug your iPhone or iPad into your Mac (or PC - the steps are essentially the same), then launch iTunes. Click on your device in the iTunes interface and select Summary. Now hold down the Alt/Option (or Shift on a PC) key, and click the Restore button

It was June 2005, and French newspaper Le Figaro announced that Apple would finally give its first step towards the mobile phone sector with a device that would be called iPhone. At that time it was said that the device would be based on the Motorola E398, that it would be white, it would reach 512 megs and would include USB support. There were false rumors of an imminent launch as well. The phone in the picture is an actual Motorola phone that came with iTunes.
Rumors went on throughout 2005, and in September the FCC approved the release of a Motorola e790 with iTunes (the previous picture). There was talk of the iPhone again, and at the end of the month, new design concepts reappeared. They predicted a conventional iPod with camera and phone capabilities.
September ended with a possible new design and another round of rumors in which Motorola president Ed Zander said that the rumors about the iPhone may be something more than that: "We know that they will have their own smartphone, it's just a matter of time". The information was accompanied by a new design in which they imagined that the iPhone would simply be a minimalist mobile phone.
In March 2006, internal sources from Benq said that Apple was contacting phone manufacturers in Taiwan to build their device. They said it would be a hybrid device between iPod and mobile phone, and that it could be released in 12 months. This mockup was designed by one "Nick C" in response to a competition Engadget held to imagine future Apple products.
On October 1, 2006 the blog appleiphone.blogspot.com published a mockup in which designer Thomas J. Mrokon imagined an iPhone that was all screen and what appeared to be a Home button.
Another mockup, designed by John Pszeniczny, was published that same day. It was closer to what the iPhone finally ended up being.
And now, more mockups...!